The ability to process complex sounds is critical for identifying and localizing most real-world objects and events, understanding speech, and producing and appreciating music. Individuals with hearing deficits can be devastated by this dysfunction which can leave them socially isolated, depressed, and even suicidal. Some forms of hearing deficits are the result of problems in the auditory periphery, in which case hearing aids and cochlear implants can be beneficial. However, these interventions have limited if any effect for those with hearing deficits due to central causes, such as strokes, brain injury, and especially natural aging. Unfortunately there are currently no established remedial therapies or treatments for hearing deficits that are caused by central dysfunction. Similarly, attention to auditory stimuli is critical for the perception of those features, although we again have very litte understanding of the neural mechanisms of these attentional influences. A better understanding of the normal cortical processes that underlie auditory perception and selective auditory attention is necessary to develop effective treatments for centrally-mediated hearing deficits. Previous research has indicated that the primate auditory cortex processes spatial and non-spatial (temporal) information independently. Specifically, it is believed that in the lateral belt auditory cortex, the anterolateral field (AL) processes temporal information while the caudolateral field (CL) processes spatial information, with the middle-lateral field (ML) processing both features in an intermediate way. To date, however, there has been no direct evidence that the activity of neurons in the lateral belt is correlated with the perception of temporal or spatial acoustic features. In the proposed study we will record single neuron activity in the lateral belt while non-human subjects attend to and actively discriminate the temporal or spatial features of identical acoustic stimuli. We will use psychophysical tasks that will engage feature-based attention in order to determine how top-down attention influences the activity of cortical neurons believed to be processing the different acoustic features, and the subject's perception of those features. These results will provide the first direct test, at the single neuro level, of the long- held hypothesis that the primate auditory cortex is composed of at least two parallel processing streams. They will also provide the first investigation of how top-down attention influences neuronal activity in the auditory cortex at the single neuron level. These experiments will distinguish between two competing hypotheses: whether attentional effects are global across auditory cortical areas regardless of which acoustic feature is being attended vs the attentional effects are selective to only those neurons processing the attended acoustic feature. Finally, these results will also provide the first test of whether attention mechanisms in the auditory system fit into the current framework of top- down attentional influences on single neuron activity that are largely based on a plethora of studies in the visual cortex.